Semiconductor component with a bipolar lateral power transistor

ABSTRACT

A semiconductor component comprising at least one lateral bipolar power transistor which is composed of at least one group of single transistors with a common collector-, base- and emitter zone, which are parallel connected by three conductor track systems which bring together the emitter-, base- and collector currents of each of the single transistors; and each single transistor comprises an emitter region having an emitter-contact zone with an emitter contact, at least one active emitter zone and a connection zone between the contact zone and the active zone, a base region having a base-contact zone with a base contact and an internal base series resistor, and a collector region, said internal base series resistor being a structured semiconductor region comprising at least two ring segments, which is connected to the base contact zone and to the base contact.

The invention relates to a semiconductor component, in particular of theplanar-epitaxial type, comprising at least one bipolar lateral powertransistor which is composed of a group of single transistors having acommon collector-, base- and emitter zone, which are parallel connectedby three conductor track systems. Said three conductor track systemsbring together the emitter-, base- and collector currents of each of thesingle transistors. Each single transistor comprises an emitter regionhaving an emitter-contact zone with an emitter contact and at least oneactive emitter zone, a base region having a base-contact zone with abase contact, an active base zone and an internal base series resistor,and a collector region.

Bipolar power transistors are customarily composed of multipleparallel-integrated single transistors which are provided withfinger-shaped conductor tracks. For this reason, these power transistorsare also referred to as multi-finger transistors. By joining themtogether, a higher output current as compared to single transistors isobtained.

Such bipolar power transistors are very robust per se. This is, forexample, ultimately the reason why bipolar power transistors are used inanalog amplifiers, peripheral data devices, electromedicine, electricvehicles, for motor ignition and motor control, for interruption-freepower supply, for switched-mode mains power supply and TV deflectioncircuits.

However, such power transistors must cope with substantial loadcurrents. These load currents generate a voltage drop as well as heat inthe component. Due to the heat generation directly associated with apower load on the transistor and the resultant temperature increase, theloadability of a power transistor is limited.

This can be attributed to the fact that as a result of a localtemperature increase of the emitter-base junction, an increase of theemitter current at the emitter base junction takes place at the locationwhere such a temperature increase, even if it is only small, occurs.This leads to a local increase in power dissipation and hence to afurther temperature rise. In this manner, an avalanche effect maydevelop which leads to breakdown.

A substantial local heat release as a result of short time loadingoutside the permissible range generally does not lead to permanentdamage, however, overloading for a longer period of time may causeirreversible damage to the transistor. This may lead to breakdown of thecomponent.

To preclude said local temperature increase, the so-termed “secondbreakdown”, power transistors are often provided with resistors in theemitter or base contact.

If resistors are provided, for example, in the emitter path of thetransistor, which resistors are connected to the emitter fingers, it isachieved that in the event of a local temperature increase and thecurrent increase primarily associated therewith, the forward voltage atthe emitter-base junction and hence the emitter current at this emitterbase junction is reduced.

DE 3035462 discloses a semiconductor element comprising at least onebipolar power transistor with parallel-connected transistor regions andwith base subregions, wherein, between active base regions at theemitter-base pn junction and contacted base regions resistors, so-termedbase series resistors, are provided, and the base current largely flowsthrough the base series resistors, and the voltage drop across theemitter region is small as compared to the voltage between the activebase region and the contacted base region.

To achieve substantially complete protection against “second breakdown”for the entire range in which operation of the transistor must bepossible, comparatively high base series resistors with correspondingisolation are required. Frequently, however, the operating conditionsare such that much lower resistance values are also sufficient, as isthe case when a large current is required and, at the same time, a smallvoltage drop at the resistor. In general it can thus be said that theselection of specific resistance values in view of specific operatingconditions of the transistor cannot guarantee optimum functioning of thetransistor under other operating conditions.

It is an object of the invention to provide, inter alia, a semiconductorcomponent with a power transistor of the type under consideration, whichexhibits a high thermal loadability, particularly in virtue of ahomogenization of the field variation, and a simple structure.

In accordance with the invention, this object is achieved by asemiconductor component comprising at least one lateral bipolar powertransistor which is composed of at least one group of single transistorswith a common collector-, base- and emitter zone, which are parallelconnected by three conductor tracks systems which bring together theemitter-, base- and collector currents of each of the singletransistors; and each single transistor comprises an emitter regionhaving an emitter-contact zone with an emitter contact, at least oneactive emitter zone and a connection zone between the contact zone andthe active zone, a base region having a base-contact zone with a basecontact and an internal base series resistor, and a collector region,said internal base series resistor being a strictured semiconductorregion comprised of at least two ring segments, which is connected tothe base contact zone and the base contact.

By virtue of the internal base series resistor, a homogenization of thefield strength and current variation is achieved. The integratedinternal base series resistors generate a negative feedback which bringsabout a uniform current distribution in the power transistor. Animpermissible temperature increase in the center of the power transistoris thus precluded.

In accordance with a preferred embodiment of the invention, the internalbase series resistor is a structured semiconductor region with emitterdoping.

By virtue of the higher positive temperature coefficient (PTC) of a baseseries resistor with emitter doping, as compared to the base region, therisk of a hot spot is reduced in that, at the hotter spots, the basecurrent negative feedback rises relative to the cooler spots and thecurrent at the hotter locations is reduced.

Particular advantages as compared to the prior art are obtained by meansof the invention when the overlay region between the base conductortrack system and the base series resistor is minimized.

Within the scope of the invention it is further preferred that theconductor track systems are formed by a single layer metallization.

In the case of a single layer metallization, the emitter cannot beconnected everywhere to the emitter conductor track system, particularlynot below the conductor track system of the individual base regions. Asthe non-contacted emitter region has a higher impedance value, it actsas an additional, negative-feedback emitter resistor.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 is a plan view of an example of a semiconductor component withpower transistors in accordance with the invention,

FIG. 2 is a plan view of a section of a power transistor shown in FIG.1,

FIG. 3 is a cross-sectional view of the power transistor shown in FIG.1.

The semiconductor component comprises a power transistor which isembodied so as to be a lateral bipolar transistor, preferably of theplanar-epitaxial type.

Said power transistor comprises a group of single transistors having acommon collector-, base- and emitter zone, which are parallel-connectedby three conductor track systems which interconnect the respectiveemitter-, base- and collector zones of the single transistors.

Each single transistor has an emitter region comprising an emittercontact zone with an emitter contact and at least one active emitterzone.

Each single transistor also has abase region comprising abase contactzone with a base contact, at least one active base zone and a connectionzone between the contact zone and the active zone.

Each single transistor further comprises a collector region.

As shown in FIG. 3, the semiconductor component of the planar-epitaxialtype is composed of a semiconductor body with a substrate 8 on which anepitaxial layer 6 is grown. In the part of the semiconductor componentunder consideration here, a buried, properly conducting layer 7 isgenerated in a customary manner between the substrate and the epitaxiallayer.

The epitaxial layer is customarily sealed from the surroundings by meansof a deep isolation diffusion and thus forms the well that accommodatesthe lateral bipolar power transistor.

For the collector, conductive contact zones are formed in the epitaxiallayer by collector deep diffusion regions indiffused from the surface,which contact zones project into the buried layer 7 and bound a longstretched-out finger-shaped collector zone which is contacted via thesecontact zones.

In the collector region there is a base zone for each single transistor,and in the base zone there is an emitter zone 3, 4 at the surface.

As shown in the plan view of FIG. 1, the active emitter zones of thesingle transistors are arranged such that in each emitter finger thereis a sequence of equal, successive structures which each form a singletransistor. In each one of these single transistors, the emitter zonecomprises an active emitter zone 4 and an emitter contact zone 3.

In the emitter region 3, 4, at the surface thereof, there is a contactedbase region 5. Said contacted base contact region 5 is centrallyarranged, and annularly encloses the emitter region 4 and laterallybounds the emitter contact region 3. Said emitter region 3, 4 is in turnsurrounded by a non-contacted base region 22.

The connection between the non-contacted base region 22 and thecontacted base region 2 is partly interrupted by series resistors 2.Said series resistors are arranged as ring segments between thecontacted base region 2 and the contacted emitter region 3.

For this purpose, between the contacted emitter region 3 and thecontacted base region 5, a segmented ring-shaped region 2 is provided,which generally has the same doping as the emitter, yet is connected tothe base potential. The base region is constricted by the segmentedring-shaped region 2.

The constricted base regions below the ring-shaped region 2 form theactual base series resistors.

Each base series resistor 2 is divided into two ring segments by twoparting lines arranged preferably in the circumferential direction atdistances of 180°. Each ring segment can also be provided, at its freeend facing away from the base contact, with a conical taper (bevel).

In accordance with a preferred embodiment of the invention, the partinglines are arranged underneath the conductor track that interconnects thebase zones. Preferably, the width of the parting lines is larger than orequal to the width of the base conductor track.

For this purpose, the parting lines have at least a width thatcorresponds to the width of the base conductor track, so that theoverlay region between the base conductor track system and the baseseries resistor is minimized.

The concrete shape of the ring segments and the parting lines is to bedetermined by the person skilled in the art. It is essential that, inaccordance with the invention, an embodiment of a base series resistorcomprising at least two ring segments is provided, said individual,adjacent ring segments preferably being situated, viewed in projection,on either side of the base conductor track.

For the purpose of providing isolation between the individual transistorregions and the superjacent conductor track systems for base, emitterand collector, which are necessary for establishing the connection, oneor more isolating layers are deposited on the upper main surface 20,which layers are not shown in FIG. 3 for clarity.

Via the apertures in the isolating layer, the emitter contact zone, thebase contact zone and the base series resistor as well as the collectorare connected to the reference potential via the respective conductortracks. Particularly for contacting the base contact region 5 and thebase series resistors 2, the contact windows 1 are provided. Saidcontact windows form common contact windows for the base metallizationand for the metallization of the series resistors.

Contacting of the base region 2 is effected by the base conductor track14. Between the non-contacted base region 22 and the surface 20 there isthe emitter region 1. Said emitter region 1 is contacted by the emitterconductor track system 13, which is customarily divided into two fingers13 a, 13 b. To contact the collector deep-diffusion regions 5, collectorconductor tracks are additionally provided.

For the collector terminal, use can also be made of a metallization onan isolating layer present on the lower principal surface of thesubstrate.

The necessary electric connections between and to the single transistorsand the contacts are preferably formed from a single, originallycontiguous metallization layer that is deposited on the passivationlayer.

The comb-shaped conductor track systems, which together with thecontacts provide the desired interconnections, are formed from themetallization layer. This requires only a single metallization level.

In the case of discrete power transistors, the same structure as thatshown in FIG. 1 can be formed, with this difference that collector deepdiffusions are dispensed with.

The planar bipolar transistors in accordance with the invention can bemanufactured, for example, by means of the standard method ofmanufacturing bipolar transistors, i.e. the SBC technique (StandardBuried Collector technique). Alternatively use can be made of theisoplanar technique.

In accordance with a preferred embodiment of the invention, the lateralbipolar transistor is an npn power transistor comprising an emitter zone3, 4 of the n-conductivity type, a base zone 5 of the p-conductivitytype and a collector zone of the n-conductivity type.

The starting material used for an npn power transistor in accordancewith the invention is a p-conductive silicon chip wherein a buried,heavily doped n⁺ layer is indiffused at locations where transistors areformed at a later stage. Subsequently, a thin, n-doped epitaxial layerhaving a thickness in the range of 2 to 18 μm is grown. By means ofp-type deep diffusion said epitaxial layer is divided into isolatedregions.

The buried layer 7 of the n-conductivity type serves to connect thecollector zone 6 of the npn transistor in a low-impedance manner. Theburied layer 7 extends parallel to the semiconductor surface. Asemiconductor zone of the n-conductivity type extending from thesemiconductor surface up to the buried layer 7 also serves to connectthe collector zone of the npn transistor in a low-impedance manner. Thenpn transistor is separated from other components, not shown in FIG. 1,by a separation zone of the p-conductivity type.

Next, in two further doping steps, the epitaxial layer for the base isp-doped and the epitaxial layer for the flat emitter is n-doped. As aresult, planar npn transistors are obtained. Thus, barrier layerisolation is employed here to isolate the collector regions.

The diffusion regions 4 structured so as to form ring segments arearranged in the base region 2. These diffusion regions 4 form theinternal base series resistor. The doping type of these diffusionregions 4 is the same as that of the emitter region 3. The diffusionregions 4 can thus be manufactured simultaneously with the emitterregion 3. Consequently, the diffusion regions 4 can be manufacturedwithout additional technology steps.

The base series resistor 2 is formed by two sub-zones situated betweenbase zone 5 and contact 1, in particular underneath the base conductortrack 14. The size of the base series resistor is set by thedimensioning of the diffusion zone. The dimensioning of the diffusionzone of the emitter as well as the location of the contacts 3 is also of( in general secondary) importance.

Finally, the surface of the semiconductor body is provided with anisolation layer that is structured such that the contact zones can beconnected. For this purpose, contact apertures are formed in theisolation layer, which accommodate metallic contacts forming theconnection to the conductor track systems. For the conductor tracksystems, preferably, a single layer metallization is provided. To thisend, a thin, closed metal layer is provided by evaporation, and issubsequently structured by means of photolithography.

Power transistors in accordance with the invention can be veryadvantageously used for applications in the low and medium frequencyrange.

1. A semiconductor component comprising at least one lateral bipolarpower transistor which is composed of at least one group of singletransistors with a common collector-, base- and emitter zone, which areparallel connected by three conductor track systems which bring togetherthe emitter-, base- and collector currents of each of the singletransistors; and each single transistor comprises an emitter regionhaving an emitter-contact zone with an emitter contact, at least oneactive emitter zone and a connection zone between the contact zone andthe active zone, a base region having a base-contact zone with a basecontact and an internal base series resistor, and a collector region,characterized in that said internal base series resistor is a structuredsemiconductor region comprised of at least two ring segments, which isconnected to the base-contact zone and the base contact.
 2. Asemiconductor component as claimed in claim 1, characterized in that theinternal base series resistor is a structured semiconductor region withemitter doping.
 3. A semiconductor component as claimed in claim 1,characterized in that the overlay region between the base conductortrack system and the base series resistor is minimized.
 4. Asemiconductor component as claimed in claim 1, characterized in that theconductor track systems are formed by a single layer metallization.